go with the simplest one! something like a dual gate FET: that's going
to ease problems with the local oscillator.
But build it as a separate module on a small PCB, and wire it in. that
way you'll be able to experimwnt later on by replacing the module. that
way you can go from easy and simple to complex and high perfoemance.
for a first it hard to beat the method. i see you're getting too much
info, especially for a newcomer!
stay in touch, I'll try to help you to the limit of my abilities.
Saaandy 4Z5KS

guys, bear in mind that the intercept point is primarily a function of
the operating quiescent poit. you cam make it high, really high and get
superlative mixers, even single ended. i designed one aroun the now
defunct VMP4 from Siliconix with an Id of 500mA!!! the damned thing had
nearly +50dB IP#. About the same went with the LNA. All in all 24W
power dissipated in the front end. How many of us can afford that or
need that for the matter?
drop it! what the guy needs is some reasonable value of dynamic range
and around 10-12 dB for IP3. he isn't going to build a radio telescope
receiver on his first attempt. Be reasonable!
with FET's the thing to ensure is that the operating point is
setablished with Vgs set at about half of the pinchoff voltage to
ensure maximum dynamic range. a noise figure under 10dB is adequate for
HF. it's not the galactic noise that limits your reception!
Saandy 4Z5KS

Hi Saandy,

I have some russian power FET similar to the VMP4 and probably better
but there is no sense to use them as they are no more in production and
diffcult to purchase in East Europe.

I believe a discussion on Mixers is important particularly for a
newcomer. He must know all the different kind of mixers than he will
have to decide.... it is like talking about small car or motobykes
because it is better run with a bicycle...one should not know about
racing car or motobykes.... he can putchase a byke tha add a little
mosquito engine or pss to a bigger motobyke or a small car later ...
but he will know what he has (he will have to push a lot with his legs
and then see to push less or not at all).... it is like for a portable
RTX were consumption is at premium... you cannot put (probably an
h-mode mixer has you will have to spend 30-50mA plus an amplifier with
other 20mA versus a NE612 that needs 3mA !!! To hell the IP3... one can
use his brain as a DSP...hi

73

Gian
I7SWX

On 28 Mar 2006 12:36:21 -0800, "Giancarlo Gian Moda, I7SWX"
wrote:


Ah..OK CSSE ... I sold a PDP11/10 with a card reader from CSS to the
Italian Goverment as a donation to a University in Peru'...the highest
PDP11 installation on the world at that time...hi

By the way, did you have to install extra fans to compensate for the
low air density (and thus lower heat carrying capacity) at high
altitudes ?

Some electronic systems have quite low maximum altitude ratings due to
this. The low air density might also cause problems for amateur radio
equipment if operated at full power at high altitudes.

Paul OH3LWR

Hi Paul,

This installation was somewhere on the Andes were there was a
astronomic site.

We did not need to use extra fans or other "helping" devices. Certainly
this set-up
was not on an open air site, it was in an building. So "air" presence
was OK for humans.

BTW, in 1966 while working in UK for a small specialized company, I was
involved in a project were we were producing the Eidofor Colour TV
Projectors (Philips Group). Philips had sold 3 of these units to be
used in Mexico City for the Olympic Games. To be sure we would not have
problems with the 3 colour tubes for explosion (I forgot M.C. height
a.s.l.) we tested the system in the BAC UK air chamber (vy expensive
tubes...hi).

73

Gian
I7SWX

Hi Allison,

OK for everything.

Please keep me updated on Art's reaction...hi

73

Gian
I7SWX

On 1 Apr 2006 00:40:31 -0800, "Giancarlo Gian Moda, I7SWX"
wrote:

Hi Paul,

This installation was somewhere on the Andes were there was a
astronomic site.

Apparently this was much before the Atacama site in Chile became
popular.

We did not need to use extra fans or other "helping" devices. Certainly
this set-up
was not on an open air site, it was in an building. So "air" presence
was OK for humans.

At sea level, the air density is about 1.2 kg/m³ and at altitudes of
4000 m (La Paz?), the air density is only 0,8 kg/m³. In a forced
cooled system, the critical parameter is the _mass_ flowing though the
system and the amount of degrees the air is heated.

In order to run the same mass of air through the system, you would
have to use 1.2:0.8 or 1.5 times the air volume in the mountains.

BTW, in 1966 while working in UK for a small specialized company, I was
involved in a project were we were producing the Eidofor Colour TV
Projectors (Philips Group). Philips had sold 3 of these units to be
used in Mexico City for the Olympic Games. To be sure we would not have
problems with the 3 colour tubes for explosion (I forgot M.C. height
a.s.l.) we tested the system in the BAC UK air chamber (vy expensive
tubes...hi).

Wasn't Eidophores used during the Apollo flights to show the orbits in
Huston ?

Paul OH3LWR

Wasn't Eidophores used during the Apollo flights to show the orbits in
Huston ?

Paul OH3LWR

Hi Paul,

I do not know but in middle of 60s that was the only TV color
projectors
designed by a Swiss engineer, assembled by Peto Scott Instrument Ltd
for Philips
in Addlestone, Surrey UK.
It was tested in the central lab were we were mainly working on
military equipments.
Many of those big blocks were sold world wide. I do remember the Mexico
Olympics
because we had to do that special test in the chamber room were
airplanes were
tested for all 3 machines.

For Peru', I believe it was somewhere over 2000 meters asl and it was
not later than 1980.

73

Gian
I7SWX

Wasn't Eidophores used during the Apollo flights to show the orbits in
Huston ?

Paul OH3LWR

Hi Paul,

I do not know but in middle of 60s that was the only TV color
projectors
designed by a Swiss engineer, assembled by Peto Scott Instrument Ltd
for Philips
in Addlestone, Surrey UK.
It was tested in the central lab were we were mainly working on
military equipments.
Many of those big blocks were sold world wide. I do remember the Mexico
Olympics
because we had to do that special test in the chamber room were
airplanes were
tested for all 3 machines.

For Peru', I believe it was somewhere over 2000 meters asl and it was
not later than 1980.

73

Gian
I7SWX